Electronic computer for division



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ATTORNEYS l4 Sheets-Sheet 10 G. R. STIBITZ ELECTRONIC COMPUTER FOR DIVISION XXXXXIIXXXXOI Feb. 1, 1955 Filed Feb. 12, 1949 I lo:

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ELECTRONIC COMPUTER FOR DIVISION Filed Feb. 12, 1949 l4 Sheets-Sheet l3 T'lg.14d 231i:@IZILQLZZ:111::IQZITIIIIIZII2121112::ZZ'JIJJII@-T2 l7 ($uBTRAus) 566 .555 (Q 1 7 300 1 1 40/ i M 631 450 I Q 400 E 37/? 575 l i 111111101100 000000101000 1 1 111111101100 000000101000 "1 01 f a 1 0-00 E 8 (A005) 366 8 3 4 6 300 g 43/ $43 409 .1- m 37/ l 3 3 I i 00000010100 000000101000 XXxxxXxxxxx 1 000000101000 000000101000 xxxxxxxxxxxo 1 (Soars/1cm) 366 OOOOOOOOOOOQ 000000101000 XXXXXXXXXYO! 000000000000 (SUBTMCTSJOOOOOOIOIOOO XXXXXXLKXXXOI 11111011000 000000101000 xxxxxxxxx01 I INVENTOR. George R SZikZ'Z BY 8 1 2%, W1UM L'V ATTORNEYS Filed Feb. 12, 1949 G. R. STIBITZ ELECTRONIC COMPUTER FOR DIVISION 14 Sheets-Sheet l4 |||||0||0000 000000101000 xxxxxxxxxou IIIIIOIIOOOQ 00000o|0|000 xxxxxxxxoug |0| 0000 000000| 0| 000 xxxxxxx'xm 0 Y I 0| 0000 000000| 0|000 xxxxxxxol |0g |||||0||0000 000000|0|000 xxxxxxx0||00 0| looog 000000| 0| 00o xxxxxxol 009 ||0| |0000 00000o|0|000 xxxxxxmlooo I m |o00g 00000010 000 xxxxxo looog w: |00o0 000000|0|000 xxxxxoHOOOO (A DB5) I m: 0000 000000| 0 000 xxxx0| IOOOOQ |0 0000 00o000| 0|000 xxxxo |00000 0| |000 000000| 0 000 mom 000000 0| 0000 0 00000| 0 000 xxxo I 000000 17 (A005) 1m IOOOQ 000000| 0|000 mm 000000 I [0| 0000 000000| 0| 000 )(XOI 10000000 18 (A005) 0 IOOOQ 000000| 0| 000 x0| |000000og 371 am 00000000000 000000000000 v 0| 000000 00 000000000000 0| |000000 00 0| 000000000 000000 000 37/ 000000000000 0000000000 IN V EN TOR.

George H. SiLbLi 8W, P LQ M, W P

ATTORNEYS United States Patent ELECTRONIC COMPUTER FOR DIVISION George R. Stibitz, Burlington, Vt.

Application February 12, 1949, Serial No. 76,088

41 Claims. (Cl. 235-61) The present invention relates to electronic digital computers and more particularly to a device for performing the division of one binary number by another.

It is an object of the present invention to provide an improved device for dividing binary numbers accurately and at a rate of speed which is far in excess of present day commercial calculators.

It is another object to provide an improved and simplified method for dividing one binary number by another in which the steps of computation require only successive additions, subtractions and shifts of a binary number relative to its binal point. It is a more specific object to provide a method of binary division in which a tally is' made of the successive additions and subtractions of a relatively shifted divisor, said tally requiring only minor correction to produce the desired quotient.

It is an object of the present invention to provide a sequential electronic computer having switches which are closed in predetermined combinations to control the flow of data in each step and in which means are provided for successively preselecting in one step the switch settings which are to be used in the following step. It is a related object to provide means capable of preselection for operating data path switches simultaneously and at precisely the beginning of a step of computation.

It is another object of the present invention to provide an electronic computer having magnetizable disks on which digits are sequentially recorded in the form of spots of magnetism and read off by an appropriate pickup head, recording and reading taking place simultaneously at different points on the same disk or on associated disks. It is a more detailed object to provide a computer having magnetizable disks in which the recording head and pickup head are advanced or retarded relative to one another in order to effect shifting of a binary number to the right or to the left with respect to its binal point.

Still another object is to provide a computer for divi sion which is relatively simple and inexpensive to construct, which is compact, and which may be advantageously utilized as a building block in the construction of computers capable of solving all normal problems of arithmetic. Neither the mechanical nor the electrical components need be constructed with extreme precision and the electrical components are, for the most part, of the standard type used in radio receivers. The number of tubes and component parts are small compared to conventional computers of comparable speed.

It is a further object to provide an improved sequential computer for binary division utilizing devices having two stable conditions of operation in which the order of the two voltage conditions to which the devices are subjected, rather than any single instantaneous condition of volt age, determines which of the two binary digits are represented. As a result, the computer may be made selfchecking and highly accurate in spite of relatively wide variations in voltage and wave form in various portions of the circuit and notwithstanding changes in the electrical characteristics of tubes and other component parts.

It is a still further object to provide a sequential computer for division having a plurality of mechanically driven elements for the storage of data and step by step solution of the problem together with a synchronized source of control impulses enabling all portions of the computer to keep in step substantially independently of variations in driving speed.

Other objects and advantages of the invention will beice come apparent from the following detailed description taken in connection with the accompanying drawings, in which:

Figure 1 is a simplified schematic diagram of the preferred arithmetic unit and memory unit employed for dividing numbers expressed in the binary system.

Fig. 2 discloses a control unit for supplying switchcontrolling impulses to the arithmetic unit and memory unit disclosed in Fig. 1.

Fig. 3 is a simplified schematic diagram of an alternative arithmetic unit.

Fig. 4 is a simplified schematic diagram of a control unit suitable for use with the arithmetic unit of Fig. 3.

Fig. 5 is a detailed view of a portion of one of the disks shown in Fig. 1, together with a typical pickup or recording head cooperating with magnetic material on the periphery of the disk.

Fig. 5a is a detailed view of a portion of a toothed pullsing disk and cooperating head for generating control pu ses.

Fig. 6 is a schematic diagram of a typical amplifier suitable for amplifying the output of a pickup head as shown in Fig. 5 and for producing a corresponding output signal of square wave form. This amplifier includes means for integrating the pickup voltage.

Fig. 7 shows a typical amplifier used in conjunction with a recording head.

Fig. 8 shows a flip-flop circuit of the type employed in practicing the present invention.

Fig. 9 discloses a typical electronic switch employed for controlling the flow of data in the arithmetic unit.

Fig. 10 discloses a simplified schematic diagram of the suiiigiing circuit used in the arithmetic units of Figs. 1 an Fig. 11 shows the wave forms existing at various signiticant points in the circuit of Figs. 1 and 2 during the solution of a practical problem.

Fig. 12 illustrates the transfer of a binary number from one disk to another without shifting.

Fig. 12a shows the transfer of a binary number from one disk to another with the recording head on the second disk displaced to produce a shift of the number to the left relative to the binal point.

Fig. 12b is similar to Fig. 12a except that the recording head is displaced oppositely to produce a shift of a binary number to the right relative to its binal point.

Figs. 13, 19a, 13b and 13c constiute a data flow diagram illustrating the flow of data in the: circuitof Figs. 1 and 2 during each step of a sample calculation.

Figs. 14, 14a and 14b constitute a data flow diagram similar to the foregoing and applicable to the arithmetic and control units of Figs. 3 and 4.

Tu the drawings a circle represents a vacuum tube switch with the arrow showing the direction of data flow, a square indicates a flip-flop circuit and a triangle, an amplifier or cathode follower. The recording and pickup heads are shown for simplicity as arrows associated with the driven disks.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail only certain preferred embodiments of the invention. It is to be understood, however, that I do not intend to limit the invention by any such disclosure but aim to cover alternative constructions and uses falling within the spirit and scope of the invention as expressed in the appended claims.

The computer to be described employs the binary system of numbers and it will be assumed that such system is sufliciently well known to persons skilled in the computer art as not to require discussion. Complete information on the binary system may be obtained from texts concerning the theory of numbers and general mathematics texts. As 18 conventional, the two binary digits employed will be referred to as 0 (zero) and 1 (one) in the discussion which follows.

Electronic computers employing binary numbers are known and have been useful in the calculation of trajec tory and for solving other lengthy mathematical proble ns. They have for the most part been relatively complicated and expensive, requiring so many vacuum tubes and related components and occupying so much space as to prohibit their use in the average business establishment. Since the computer disclosed herein acts upon successive binary digits sequentially and in a novel manner to produce the quotient of a problem in division, the number of electronic components is much smaller than previously required for the solution of practical problems. For this and other reasons the present computer will be found to be eminently suited for use in industry in performing payroll calculations and the like. By adding only a few components and by employing a novel scheme for multiplication as covered in my co-pending aplication, Serial No. 157,369, filed April 21, 1950, on Computer for Multiplication, it is possible to adapt the present computer to perform all normal arithmetic problems. The computer to be discussed is well adapted for use as a building block in the construction of computers to solve problems of almost any degree of complexity.

For purposes of convenience. the computer will be arbitrarily divided into three sections which may be termed the memory unit. the arithmetic unit and the control unit. The memory unit serves to store the raw data in the form of spots of magnetism on a movable magnetic element, preferably a rotating disk. Pickup and recording heads are used in cooperation with the disk or the like to read off the data as required in the solution of a mathematical problem and to later record the answer. Both of these operations are controlled by operating electronic switches associated with the recording and pickup heads. It will be assumed in the following description that data has previously been recorded on the disks in the memory unit by any desired means.

The arithmetic unit receives the raw data from the memory unit in the form of a series of voltage impulses, modifying it in a predetermined manner to produce the answer to a problem in division. The procedure for acting upon the data is partially determined by means of a set of c ntrol data previously recorded on magnetic tape or the like. The answer is recorded in the form of magnetic spots on a disk which may, if desired, be the same as that from which the problem data was previously read. Durin the course of arriving at an answer to a problem, electrical impulses corresponding to the recorded spots of magnetism and in the form of discrete voltage waves or couples are routed in a predetermined manner through the arithmetic unit, being successively recorded on and read from rotating magnetic disks. In performing the process of division, a summing circuit is used to obtain the sum of or difference between the various binary numbers involved. Moreover, binary numbers are multiplied or divided by two, in other words, shifted to the left or right relative to the binal point, by proper placement of the recording and pickup heads about the periphery of the magnetic disks.

The routing of the binary numbers through the summing circuit and through the multiplying and dividing disks, as well as through the various other circuit components, is controlled by the control unit. The latter includes means synchronized with the memory disks for unlocking the switches in the arithmetic unit in proper sequence and for the proper time interval. It will be appreciated, however, by one skilled in the art that the unlocking sequence is not completely predeterminable but is dependnt upon the condition of the data during the intermediate steps in the solution of the problem. The arithmetic and control units thus may be said to interchange data between them to effect a solution. Throughout the discussion which follows it will be understood that data is represented electrically in the form of voltage couples just as in the computer described in my co-pending aplication Serial No. 34,968, filed June 24, 1948, on Computer for Addition and Subtraction, and which issued at Patent No. 2,609,143 on September 2, 1952. A binary 1 may be represented by a plus-minus couple, while a binary is represented by a minus-plus couple. Similarly, a binary 1 may be magnetically represented on a disk by a north-south magnetic couple, while a binary 0 is represented by a south-north couple. In short, the sequence of the voltages (or magnetic polarities) comprising a couple and not the magnitudes thereof determines the binary digit. Reference is made to the above application for discussion of the advantages inherent in this manner of representing data.

4 PROCESS OF DIVISION In the practice of the present invention, the process of obtaining the quotient of two binary numbers differs from what is conventionally known as long division. Instead I have found that the process of obtaining a quotient may be performed by first adjusting the magnitude of the divisor relative to the dividend and then performing a series of additions and subtractions of the divisor from the dividend and from the successively produced remainders with the divisors shifted relatively one place to the right after each addition or subtraction. A binary 1 is tallied whenever a subtraction is performed and a binary 0 for each addition to produce an uncorrected quotient; then a number of simple corrections are performed to produce a true, corrected quotient. More specifically, the steps which are performed by the computer disclosed herein in obtaining a quotient are as follows:

(1) The numbers are preliminarily adjusted to the right or left. The first and most important adjustment is to shift one of the numbers so that the divisor is larger than the dividend, making a quotient of less than unity. The mathematical justification for this will later appear. In order to achieve maximum accuracy the relative adjustment should cause the numbers to be as nearly as possible equal in magnitude, consistent with producing a quotient of less than one. The net shift should be noted, enabling a corresponding change to be made in the quotient after it is obtained. To further insure accuracy, and to make full use of the capacity of the machine, the numbers should be moved jointly to the left as far as possible. Shifting all the way to the left is to be avoided, however, since the high order digit is employed for rcpresenting sign.

(2) Next a novel division-like process is performed in which the divisor is first subtracted from the dividend. Upon making such subtraction, a binary 1 is noted as the first digit in the uncorrected quotient. This initial binary 1 is always discarded as an incident to obtaining the final answer and therefor need not be recorded and is not recorded in the present computer. The subtraction produces a negative remainder. The divisor is next shifted one place to the right relative to the remainder. Since the remainder from the previous step is negative, the shifted divisor is algebraically added thereto to produce a new remainder. Because an addition was performed, a binary 0 is tallied or recorded as the second digit in the uncorrected quotient. The divisor is again shifted to the right relative to its binal point and applied to the remainder from the previous step. If the remainder is negative, addition is performed and a binary 0 is entered as the next digit in the uncorrected quotient, while if the remainder is positive, the divisor is subtracted and a binary 1 is entered in the uncorrected quotient as the next digit. This process is repeated, each time shifting the divisor one place to the right and either adding it to or subtracting it from the previously obtained remainder. In this way, the remainder will be constantly reduced in magnitude, although it may either be positive or negative in sign. This process is repeated until the desired number of binal places has been obtained in the uncorrected quotient.

In the invention in its preferred form negative binary numbers are indicated by the complement. The capacity of the computer is sufiiciently great so that there will be one or more idle spaces in the higher orders filled up with binary Os when the number is positive and binary ls when the number is negative. The digit of highest order in the remainders thus may be utilized as an indicator of sign and, more importantly, as a tally of whether the shifted divisor is to be added or subtracted. In carrying out the improved method of division it will be seen that the high order digits of the respective remainders when inverted become the digits of the quotient.

(3) The uncorrected quotient obtained as the result of the foregoing operation has the form 1.0 the spaces to the right of the O constituting the significant digits in the answer. Such uncorrected quotient is next corrected by shifting it one place to the left relative to the binal point and then disregarding those digits to the left of the binal point. (As was mentioned earlier, in the computer described herein, the 1 resulting from the initial subtraction is not recorded since it is not required for the significant digits of the answer.) This produces a semicorrected quotient which consists of the correct significant digits but which must be further corrected in order to compensate for the adjustment of the binal point made in step (1). Thus, assuming it was necessary in step (1) to shift the dividend one place to the right relative to its binal point in order to make it less than the divisor, the quotient should be shifted one place to the left to compensate and to produce a final corrected quotient.

MEMORY UNIT The memory unit used for storage purposes in the present computer is indicated at 20 in Fig. 1. It includes a rotating disk 21 having a magnetic periphery on which the data is stored in the form of north and south couples of magnetism. This disk is rotatively driven by means of a shaft 27 powered by a driving motor 28 which rotates at a nearly constant speed which may be on the order of 1800 R. P. M. Cooperating with the periphery of the disk 21 is a recording head 30 which serves to magnetize the disk in response to variations in the exciting current. 'Spaced around the periphery from the recording head 30 is a pickup head 31 which produces a voltage corresponding to the polarity of the magnetic spots on the disk. With regard to the disk and cooperating heads, reference is made to Fig. where it will be noted that the head 30 on the disk has a core structure 30a and a pair of coils 30b, the magnetism being concentrated in the narrow air gap 30c along successive elements of the disk periphery. When the head is used for pickup purposes, the coils are arranged in series for greater sensitivity. However, when the head is used for recording purposes, the coils are separately and oppositely energized. More detailed discussion of this portion of the apparatus is to be found in my co-pending ap' plication Serial No. 34,968, filed June 24, 1948.

In order that recording may take place at a reliably high level, the recording head 30 is energized by a recording amplifier 33. As shown in Fig. 7, such amplifier preferably includes a pair of vacuum tubes 34, 35, the plates of the latter being connected directly to the coils 30b. The input lead 37 is connected to the grid of the tube 34, while the grid of the tube 35 is controlled by the plate circuit of a tube 34. A diagonally connected resistor 38 associates the plate of the first tube with the grid of the second. It will be apparent, therefore, that when a positive voltage is applied to the grid of the tube 34, a large amount of plate current will be drawn energizing the left hand coil 30b on the head. Simultaneously, the plate of the tube 34 swings negatively, thereby reducing the flow of plate current in the opposite leg 30!). Conversely, when a negative voltage is applied at the input, the tube 34 becomes non-conducting and the tube 35 heavily conducting, resulting in a reversal of the magnetism in the core 30:! of the head 30. In this way, a plus-minus voltage couple applied to the input results in the recording of correspondingly polarized spots of magnetism on the disk as the latter rotates.

Since the amount of magnetism which may be imparted to the disk is rather small, it is necessary to amplify the output of the pickup head 31. This is accomplished in the pickup amplifier 39 which is set forth in schematic form in Fig. 6. As the magnetized spots on the disk 21 are moved past the air gap, the flux set up in the magnetic circuit thereof induces a voltage in the coil proportional to the rate of change of flux. The latter voltage is applied to the input terminal 40. After amplification by a tube 41, this voltage is integrated by a capacitor 42 and resistor 43, the voltage across the capacitor being then proportional to the flux. This voltage is further amplified by tubes 44, 45 and 46 and applied to the grid of the following stage. This following stage consists of a flip-flop circuit having tubes 47, 48. The plate of the tube 48 is connected to the output terminal 49 of the amplifier. The flip-flop circuit remains in one of two stable conditions except when a positive unlocking pulse is applied. This unlocking pulse is received through an unlocking terminal s which is connected to a cathode follower 51. The output of the latter is connected to the cathode terminals of the flip-flop tubes 47, 48. Whenever an unlocking pulse is received at the unlocking terminal s, both of the tubes in the flip-flop circuit are cut off and become non-conducting. When the unlocking pulse in removed, the flip-flop stage will assume a condition which is dependent upon the then existing condition of the voltage at the input. As will later appear, the flip-flop stage receives an unlocking pulse once for each magnetized spot on the disk 21 so that the output of the pickup amplifier at 49 is a full square wave of voltage for each digit.

During the normal operation of the computer, the voltage output of the amplifier 39 is fed into an output line or bus 59 via a switch 56. When the switch 56 is closed, the signal from the disk will be applied to the input line 59, with similar switches being used to feed the data into other portions of the circuit. When it is desired to feed data from the line 59 onto the disk 21, the circuit from the line to the recording amplifier 33 is completed through a switch 60. To re -record a number on the disk 21 in shifted position, it is sulficient merely to close the switches 56, 60 to form a simple loop circuit.

The schematic diagram for the switches 56, 60 is to be found in Fig. 9, the switch 56 being taken as representative. In its simplest form it includes a pair of triodes 65, 66 having a common cathode resistor 67. The operation of the circuit is as follows. When the control lead 57 is positive, the triode 66 conducts heavily through the cathode resistor 67, thereby biasing the other triode to cutoff. Under such conditions, the output voltage remains constant regardless of the variations in the input and the switch may be considered off. Conversely, when a negative voltage is applied to the control terminal 57, very little current flows through the cathode resistor 67, and the variations in the output voltage correspond to the variations in voltage at the input terminal 49. The switch is then on. There will, of course, be a 180 phase reversal in the switch, but this is unimportant since it may be compensated for merely by taking the input for the switch from the opposite plate of the flip-flop circuit feeding it. In some cases, a switch may not derive its input: directly from a flip-flop, but in these cases the phase can be reversed at some other point in the circuit before it is again recorded on a disk. The switch illustrated is preferred since it is simple and reliable. However, it will be apparent to one skilled in the art that other specific electronic switches may be employed which include no phase reversal without departing from the invention. Also, additional units such as the unit 20) may be connected to the bus 59 in exactly the manner shown in Fig. 1. For the sake of simplicity, however, only one memory unit will be sufficient to understand the operation and to solve a typical problem.

ARITHMETIC UNIT The arithmetic unit occupies the remainder of Fig. 1 and has been given the general designation 70. This unit is fed data in the form of voltage couples from the memory unit 20 via the line 59 and is arranged not only to add and subtract binary numbers, but also to shift numbers relative to the binal point between the various additions and subtractions, producing an answer which is the quotient of two binary numbers appearing successively at the input terminals. The successive steps in which such mathematical operations take place are determined by the setting up of the switches located throughout the circuit in various combinations. Both the control unit for controlling the operation of such switches and the mathematical justification for the various operations employed to produce the answer to a problem of division will be covered in subsequent sections It will be useful at the outset to describe the arithmetic unit 70 purely from the standpoint of the physical components contained therein. In the present embodiment, four disks are used, all of these being rigidly mounted on the rotating shaft 27. The first disk 71 is used for temporary storage of data between successive mathematical steps and has associated therewith a recording amplifier 72 and a pickup amplifier 73. For purposes of convenience the disk is divided into four quadrants with space for the recording of four binary numbers. In the example to follow it will be assumed that each number is 12 digits in length, although computers of this type may be constructed to accommodate numbers 25 digits in length or even longer. It will be convenient in referring to disk 71 to speak of it as having four number spaces on its periphery each made up of 12 digit spaces. These terms will also for convenience be applied to the time intervals required for rotation of the disk through corresponding degrees of arc.

The next disk is a multiplying disk 74 which is employed for retarding a binary number one digit, in

other words, for shifting the number one binal place to the left. For this purpose, the recording head 75 associated therewith is retarded or backed off one digit space relative to the pickup head. As in the previous stage, the disk 74 has a recording amplifier 76 and a pickup amplifier 77 associated therewith. The latter amplifiers are essentially the same as those previously described in connection with Figs. 6 and 7.

The next disk rigidly coupled to the shaft 27 is the disk 80. This disk may be termed a dividing disk since it is employed to shift a binary number to the right one space relative to the binal point. To this end, the recording head 81 is advanced about the periphery one digit space in the direction of the pickup head. A recording amplifier 82 is used which is similar to the recording amplifiers previously discussed. The pickup amplifier 83 is also similar to the previously-mentioned pickup amplifiers shown in Fig. 6 except that it includes two output terminals, a direct lead 84 and an inverted lead 85. Referring to Fig. 6, these output terminals are connected to the respective plates of the tubes 47, 48 in the flip-flop circuit. The voltages applied thereto will thus be equal, but opposite in polarity or phasing. The direct lead 84 is connected to the main bus 59 by means of a switch 86.

The remaining disk shown in Fig. 1 may be termed a zero generating disk, and has been designated by the numeral 90. This disk is permanently magnetized with a series of magnetic couples representative of binary Os or, if desired, may include magnetized teeth. This disk has a pickup amplifier 91 in its output circuit having dual output leads 92, 93 just as discussed in connection with the amplifier 83. With the amplifier 91 unlocked by application of voltage to an unlocking terminal, a series 'of couples representative of binary Os will appear on the lead 92, while a series of couples representative of binary ls will appear on the lead 93. The flow of these digits into the remainder of the circuit is under the control of switches to be subsequently discussed. The components 90-93 referred to form a part of a digit inserter. The purpose of the digit inserter is substantially the same as set forth in my co-pending application Serial No. 157,359 of which mention has been made, namely, to fill in binary Os wherever required and to add a low order binary 1 in obtaining the complement of a binary number. In the case of each of the pickup amplifiers 39, 73, 77, 83, and 91, unlocking takes place in unison at each half of the couple to produce a square wave output. Consequentlv. all of the unlocking terminals have been designated with the letter s and all are pulsed in unison. The means for supplying the unlocking pulse will be discussed in connection with the control unit (Fig. 2).

The addition and subtraction of binary numbers as required in the process of division is performed by a summing circuit 100 shown at the bottom portion of Fig. 1. This circuit includes a first input lead 101 and a second input lead 102 which carry the respective binary numbers to be added. The voltage couples representative of the sum appear at the output lead 103, being subsequently conveyed to a rotating disk and there at least temporarily recorded. Digits for insertion in the lowest order for corrective purposes are supplied through a lead 104 while control voltages for controlling the insertion of such digits are applied to leads 105, 106. As covered in the above-mentioned applications, it is also necessary to suppply a summing circuit 100 with control pulses for operating a delay chain to enable the carrying of a digit from one order to the next higher order. These pulses are supplied on leads 107, 108. The terminals for the control and pulse leads have been designated 11, 0, s, and t respectively, and are supplied from correspondingly lettered terminals in the control unit (Fig. 2). The specific circuit employed in the summing circuit 100 will be described in connection with Fig. 10.

A complete calculation takes place in a 'SCIICS of steps, and paths are provided in the circuit to insure that the data flow takes place in each step in a predetermined manner between the rotating disks and summing circu t. Such paths are provided by a plurality of ele ctron1c switches, each having a control terminal WhlCh 1s controlled by the control unit to cause the circuit to be closed or open. The switches are identical and have a clrcuit corresponding to that which was previously discussed in connection with Fig. 9. The switch 110 controls the flow of data from the disk 71 to the input lead 101 of the summing circuit. The switches 111, 112, 113, 114, 115, 116 are used in the input or recording circuit of disk 74. Similarly, the switches 120, 121, 122, 123 are used at the input of the dividing disk 80 to enable data to be controllably fed thereto from various portions of the circuit. Each of these switches is operated by the fondtrol unit and has a correspondingly lettered control In order to enable the summing circuit to effect a subtraction of two binary numbers, switches are provided at the input lead 102 to enable a binary number or its complement to be used. These switches are associated with leads 84, 85 and have been designated 124, 125 respectively. Further, it is desired that the low order digit used for corrective purposes and entering the summing circuit by a lead 104 be either a binary 0 or a binary 1. For this purpose a switch 126 connects the summing circuit to the lead 92 from the zero generating disk 90 enabling a binary 0 to be fed into the summinr circuit while a second switch 127 may be closed to connect the lead 93 which carries a series of binary ls. It will be understood, of course, that only an initial couple corresponding to a binary 0 or 1 will be required for a given step in the calculation.

Completing the diagram of Fig. 1, an inverter 130, used for writing a quotient digit in anticipation of what is to be done in the next step, is connected to the output of the summing circuit. The information therefrom may be recorded on disk 74 via switches 111, 113. Switch 113, however, will be turned on to record only the high order digit. Also associated with the write lead 103 is a switch 131 which enables the write signal to appear on the main bus 59 for recording the same on disk 21 or 71. In order that data might be fed from the arithmetic unit to the control unit for controlling the intermediate operations of the latter, the write lead 103 of the summing circuit is fed through a locked two-condition device 132 having an output lead 133 leading to a terminal in. This device includes an unlocking lead 134 having a terminal 1'. The latter terminals, just as in the case of the other control terminals in Fig. l, are lettered to correspond to the output terminals of the control unit (Fig. 2).

Operation of the two-condition device 132 will be apparent by reference to the schematic diagram in Fig. 8. Here it will be noted that the circuit is somewhat similar to the well-known Eccles-Jordan flip-flop circuit, using a pair of triodes 135, 136 having diagonally coupled grids and plates. Thus the circuit will remain in one of its two stable conditions, namely, with one of the triodes conducting heavily and with the remaining triode substantially non-conductive. The device diflers from the conventional Eccles-Jordan circuit however in an important respect. In the latter circuit application of a positive pulse causes the circuit to switch from its existing stable condition to its alternate condition. Each pulse results in a change of condition. In the present device, by contrast, a separate input lead is provided, here input lead 103, which controls the condition to be assumed by the circuit and the pulse lead 134 simply unlocks the circuit so that the input lead may assert itself. More specifically, with the circuit arranged as shown, the input lead 103 is ineffective to establish control, and the voltage thereon may change back and forth without affecting the condition of the circuit. However, when a positive or unlocking pulse is applied to the lead 134, both tubes become momentarily non-conducting and the subsequent condition of the circuit, i. e., which tube will conduct, depends upon the then-existing voltage on the input lead.

Turning now to the summing circuit 100 in the arithmetic unit, the schematic diagram will be found in Fig. 10. This circuit may be conveniently broken down into a digit adder 140, included within the dotted outline, a carry delay chain 141 and switches 142, 143 used for low order digit insertion. The digit adder is essentially the same as that disclosed in Fig. 11 of my abovementioned co-pending application Serial No. 34,986, the input terminals being designated A, B, C and A, B, C to correspond thereto. These terminals carry the respective direct and inverted input signals. Inversion is accomplished by any desired phase-inverting amplifier, the three amplifiers used in the present circuit being designated 145, 146, 147. Suffice it to say that voltage couples representative of binary digits are simultaneously applied to the input terminals 101, 102. The sum then is passed through a conventional cathode follower 149 and appears at the write output lead 103. Any carry digit resulting from such summation appears at the carry output lead 148 and is appropriately delayed by the carry delay chain 141 until the instant when the digit adder is ready to sum up the digits of the next higher order. At such time the digit which has been carried, and which is either a binary 1 or a binary 0, is applied through the switch 142 to the carry input leads CC.

Insertion of the digit which has been carried is precisely synchronized with the digits entering the summing circuit by leads 101, 102 by means of the four serially arranged flip-flop circuits 150153. These are successively unlocked at intervals of a quarter of a digit space by means of accurately timed unlocking pulses applied to the leads 107, 108. In order to insure positiveness of operation, amplifiers 154-158 are used at the beginning of the carry delay chain and in series with the unlocking leads.

As described in my aforesaid Patent No. 2,609,143 of September 2, 1952, it is necessary to insert a binary into the digit adder in place of the carry signal for the low order digit when two positive numbers are to be added; and it is necessary to insert a binary 1 in place of the carry signal for the first digit of a subtraction problem when the complement of one number is to be added to another number. Such low order digit insertion can be readily effected in the present circuit by opening the switch 142 and closing the switch 143 just prior to the first digit space, whereupon a binary 0 or 1 will be applied to the carry input leads CC. As previously noted in connection with Fig. 1, whether a binary 0 or a binary 1 is inserted, is determined by the selection of switches 126, 127.

CONTROL UNIT As was stated in connection with Fig. l, the process of division takes place in a series of steps and for each one of these steps data must be routed in a predetermined manner through selected paths in the arithmetic unit. Each step thus requires the applicable switches to be preset at the instant that a given step begins and, in general, to remain set until the beginning of the next step at which time a different combination of switch settings is required. This is one of the primary functions of the control unit which is set forth in block form in Fig. 2.

The control unit includes a series of control disks which are mounted for rotation with the shaft 27. The shaft 27 is, of course, an extension of the shaft which is shown in Fig. 1. This shaft also serves to drive a member which carries stored program or control data for setting the various switches in the arithmetic unit. Preferably such data is stored magnetically spaced along a tape 170. The latter is driven through a sprocket 1'71 which is coupled to the shaft 27 by means of a clutch 172. This is to enable the tape to be stopped and started at will in synchronism with the feeding of problem data into the remainder of the computer. Preferably, the tape 170 includes the data in the form of magnetic spots arranged in the form of north-south or south-north magnetic couples just as on the periphery of the data disks of Fig. 1. To compensate for different lengths of control tape which might be required for different programs of calculation, the tape is passed over a takeup mechanism 173. Control impulses are read from the tape by means of the pickup head 174 and associated amplifier 175. The latter may be of conventional type, producing a sinusoidal output which corresponds to the variations in flux along the tape.

Prior to discussing the main portion of the control unit, it will be helpful to refer briefly to the means here used for controlling the clutch 172. This clutch is a socalled B clutch which is energized upon the application of voltage to an input lead 176. The clutch itself is discussed in considerable detail in United States Letters Patent No. 2,013,649 dated September 10, 1935. Since the shaft 27 normally rotates at a speed on the order of 1800 R. P. M., it is, of course, necessary that the clutch be both rapid and positive in engagement and it is further desirable for foolproof operation that the clutch be energized at a predetermined phasing relative to the positioning of the shaft 27. This is accomplished in the present instance by means of a clutch control disk 180 having a single magnetic discontinuity, here tooth 181.

The latter sweeps past a pickup head 182 once per revolution, changing the reluctance of the pickup head and producing a voltage impulse which is amplified by an appropriate amplifier 183. The pickup head 182, as well as the remaining pickup heads used in conjunction with toothed wheels in the control unit, is shown in detail in Fig. 5a. The head may be quite similar to that shown in Fig. 5. A bar magnet 189 or the like is used to provide a steady state flux. The amplifier 183 may, if desired, include means for peaking the output. Regardless of the type of amplifier or peaking means used, it is desirable that the output pulse be both abrupt and large in amplitude so that positive operation of the control switches or flip-flop circuits is assured.

The output of the amplifier 183 serves to unlock a flip-flop device 184 having input leads 185, 186 and an output lead for feeding into the clutch control lead 176. This flip-flop device may be the same as that disclosed in Fig. 8 except that the additional input lead is connected to the grid of the second tube. A switch 188 in the input circuit enables a positive switching voltage to be applied to either of the input leads. In operation, throwing the switch to the on position will, of itself, have no effect until the flip-flop circuit is unlocked by a pulse derived from the disk 180.

In accordance with one aspect of the present invention, two series or layers of flip-flop devices are provided for setting the switches in the arithmetic unit. These include a first series 200 of conditioning flipflop circuits which are set, one by one, in predetermined conditions of equilibrium during one step of computation and a second series 201 set by the first series simultaneously and at the beginning of the succeeding step. The means here employed for setting the switches of the first series, one after another, may be referred to as a successive unlocking device 202 since it unlocks the flipfiop circuits in the first series so that they may be responsive to the respective conditions indicated at corresponding points on the control tape 170.

The preferred unlocking arrangement employs a delay chain 203 which includes a series of flip-flop circuits 204-215. Taking the first flip-fl0p device 204 as representative, it will be noted that it includes an input lead 220, an output lead 221, and an unlocking lead 222. The specific circuit corresponds to that shown in Fig. 8 previously discussed.

Prior to the beginning of a step of computation, the flip-flop device 204 receives a voltage pulse from an initiating pulse disk 223 having teeth 224 thereon which are spaced at intervals corresponding to the length of a number space. Since there are four number spaces per revolution, four teeth are used. The passage of the teeth 224 adjacent a head 225 gives rise to voltage couples which are amplified in the amplifier 226.

The flip-flop device 204 will not, however, respond to the pulse from the amplifier 226 unless it is first unlocked by applying a positive pulse to the unlocking lead 222. Let us next see how the unlocking pulses are derived for unlocking the flip-flop device 204 and the sub sequent flip-flop devices in the delay chain. These unlocking pulses are obtained from an unlocking disk 230 having teeth thereon which are spaced at two-digit intervals. Each of the pickup heads 231, 232 associated therewith produces a generally sinusoidal voltage wave whenever a tooth sweeps past. The two heads are located about the periphery at such spacing that voltage pulses are generated alternately therein. Peaking amplifiers 233, 234 are connected to the respective heads.

The practical design of such amplifiers is well within the capabilities of one skilled in the art. In a preferred embodiment the amplifiers contain circuits for squaring the unpeaked voltage pulses generated in the pickup head and then differentiating these squared voltages to obtain sharp peaks. The negative peaks are then removed to leave only positive peaks spaced two digits apart. For a discussion of wave shaping circuits, see Basic Course in Electrics, published by the U. S. Naval Institute, 1948, chapter XIX at page 207. Positive pulses are thus applied to output leads 235, 236 alternately at the beginning of alternate digit spaces. It will be noted that the output lead 235 is connected to flip-flop devices 204, 206, 208, 210, 212, 214, while the output lead 236 is connected to the intervening flip-flop devices, namely. 205, 207, 209, 211, 213 and 215.

The passage of a pulse step-by-step down the delay chain will be made clear by considering the normal operating sequence. As the first flip-flop device 204 receives an initiating pulse from disk 223, it is unlocked so that the output lead 221 thereof assumes a condition corre sponding to that of the input lead 220. One digit space later the next flip-flop device 205 is unlocked allowing it to respond to the then reversed ouput voltage of the first flip-flop device 204. One digit space after that, the flip-flop device 206 is unlocked and it responds to the then existing output voltage of the flip-flop device 205 immediately ahead of it. At the same time flip-flop device 204 is unlocked. Since the tooth 224 is now past the pickup coil 225, the voltage on lead 220 will have returned to normal and flip-flop device 204 will therefore change back to its normal condition. In this way each of the flip-flop devices in the delay chain 203 produces a voltage pulse at its output which is two digit spaces in length and spaced from the pulse generated by the preceding flip-flop by a time interval of one digit space.

As stated above, the pulses, spaced in time, obtained from the delay chain are used to sequentially unlock the series of conditioning flip-flop devices 200. However, since the duration of the pulses obtained from the delay chain is too long, on the order of two digit spaces, means are provided for narrowing down the time interval over which the conditioning flip-flop devices are unlocked. The latter is accomplished by a series of switches 250261.

Taking the switch 250 as representative, it includes an input lead 262, an output lead 263, and a control lead 264. The circuit of each of the switches corresponds in basic design to that previously discussed in connection with Fig. 9, except that the inherent reversal of polarity occurring in the switch may be compensated for by merely inverting the output. While it is true that each of the switches receives an input pulse a number of times during each step of computation, such pulses will only appear at the ouput when the switch is on. The latter condition occurs only once during each step. The delay chain 203 and the associated switches thus cooperate in a novel manner to produce accurately timed pulses which are suitable for synchronization with the control tape 170.

As will later appear, it is desirable that certain switches in the arithmetic unit (Fig. 1) operate prior to the beginning of a step of computation. It is necessary therefore to advance the disk 223 slightly with respect to the shaft 27. This should be an amount sufiicicnt so that the output pulse from switch 250 occurs one digit space prior to a step of computation, with the output pulse from switch 251 signalizing the beginning of a step of computation. The pulse from switch 250 may be referred to as the 1 pulse while that from 251 is referred to as a number pulse.

Associated with switches 253-261 are the individual conditioning flip-flop devices comprising the first series and designated 270278 respectively. All of the latter, it will be noted, are simultaneously energized on the input side by a line 279 coming from the pickup head 174 of the control tape. They cannot, however, all respond simultaneously to the voltage impulses on the line 279 since they are unlocked only one at a time. Each of the devices 270278 may be considered to have a control space reserved for it on the tape 170, the tape being so phased that such space passes the head 174 just as the corresponding flip-flop device is unlocked. Since the synchronizing elements are mechanically coupled, a high order of accuracy may be achieved. By the end of one step of computation each of the flip-flop devices in the first series, or layer 200, has been energized by the control tape to assume the condition suitable for the next step. As a result the proper combination of voltages is caused to exist on the output leads 280-288 which interconnect the two layers 200, 201.

The flip-flop devices which are in actual control of the switches are designated 291298 and have specific circuits similar to that shown in Fig. 8. These do not change their condition immediately upon a change of condition in the leads 281288 which supply them, but require unlocking. In practicing the invention, the switch controlling flip-flops are unlocked simultaneously at the very beginning of a step of computation. They are then free to respond to the associated conditioning flip-flop devices, such response taking place instantaneously to cause the immediate setting in the switches of the arithmetic unit. It may be noted at this point that the flipflop device 291, and 270 as well, differ from the circuit of Fig. 8 only in that a second output lead is provided from the plate terminal of the left hand tube 135.

Consideration may next be given to the means employed for simultaneously unlocking all of the flip-flop devices in the second layer 201. It will be observed in Fig. 2 that the switch 251 which is unlocked by the flipflop device 205 feeds into a lead 299 which is connected to the unlocking leads of all of the flip-flop devices in the second or output layer. As a result of the simultaneous unlocking, it will be apparent that the switches in Fig. 1, having control terminals b, c, d, e, f, g, h, i. j, will be open circuited or short circuited in a predetermined manner to meet the needs of the ensuing computation step.

The components thus far described are capable of setting the switches in the arithmetic unit at the beginning of a step of computation. There are certain switches required for low order digit insertion which must be operated one digit space in advance. To this end a pulsing disk 310 is used having four teeth 311 which sweep adjacent a head 312. The voltage induced therein is amplified in an amplifier 313, and applied to an output lead 314, which leads to flip-flop device 315. The latter has output terminals p, q which are connected to correspondingly lettered terminals in the arithmetic unit of Fig. 1.

With the disk 310 properly advanced in the direction of rotation, the pulses appearing on the lead 314 may be made substantially one digit space early. Means are additionally provided, however, for increasing the timing accuracy of the voltages applied to the terminals p. q when the condition of equilibrium of the flip-flop device 315 is reversed and then restored to its original condition precisely one digit space later. This is accomplished by connecting the unlocking lead 307 of the flipflop device to two sources of pulses, spaced one digit space apart and timed by the same pulsing disks 223, 230 which control the remainder of the computer. in the present instance the unlocking lead 307 is supplied from lead 263 via an amplifier 308 and from lead 299 via an amplifier 309.

In operation a pulse approximately one digit space in length is supplied to the device 315 from the disk 310 slightly more than one digit space prior to the start of a step of computation. The device 315 is unlocked exactly one digit space prior to the start of a step of computation. This causes it to flip into its alternate condition in which it remains temporarily even though the voltage on the input lead 314 reverts to its former value. One digit space later another unlocking pulse causes the device to flop back to its former state.

In similar fashion, it is desirable to produce special pulses at the beginning of a step of computation and exactly one digit space later for what will be referred to as high order digit insertion. This is accomplished in the present instance by disk 320 having four teeth 321, and associated pickup head 322. The output of the amplifier 323 is fed into a lead 324 which is connected to the input of a flip-flop device 325 having output leads 326. This flip-flop device 325 is unlocked at the beginning of a number space by a signal from unlocking lead 304 via an amplifier 305 causing predetermined voltages to appear on terminals n, 0. One digit space later it is restored to its original condition by an unlocking pulse applied to lead 304 by an amplifier 306 As will later appear, it is necessary to unlock flipflop device 132 (Fig. 1) at the last digit of a number space in order to determine whether the ensuing step is to be addition or subtraction. Such unlocking is accomplished by the disk 330 having four teeth 331 thereon. Voltage induced in a head 332 is amplified by amplifier 333 and fed into a lead 334 connected to the terminal r. More will be said of the function of the pulse appearing at terminal r in the example to follow.

The remaining disk in Fig. 2 is employed to unlock the delay chain 141 included in the summing circuit 100. This disk is designated 340 and includes a plurality of closely spaced teeth 341, one per digit space. Cooperating with the teeth is a head 342 feeding into an amplifier 343 having both direct and inverted output leads 344, 345 respectively. These output leads are connected to the terminals designated s, t. The amplifier 

